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This is why you shouldn’t work out on an empty stomach

Written By The Good Housekeeping Web team | 24 March 2017

Other than the fact the person next to you on the treadmill doesn't want to hear your stomach rumbling.

Most people probably think you should avoid eating directly before a gym work out. Not only because morning work-outs can feel more effective, or because all that vigorous movement on a full stomach could leave you feeling nauseous; but also because some people believe if they don't carb-up pre-gym, the exercise will burn excess body fat instead of the stuff you've just put in your system.

And that way of thinking definitely makes sense where both logic and science are concerned; there have, after all, been studies carried out which indicated participants burned an average of 20% more body fat by exercising in a fasted state.

But as LifeHacker quite rightly points out, there are actually a few really big catches to this. They spoke to sports dietetics specialist Kelly Pritchett, Ph.D., R.D., who explained that when you start to burn fat rapidly - as one would if they exercise on an empty stomach - your body starts to adapt, adjusting your metabolism so it's in line with the fat burning. Essentially, it'll start going into "survival mode", slowing your metabolism right down and causing you to burn fewer calories. Exactly the opposite of what you're trying to do if you're exercising to lose weight.

There's also another benefit to fuelling your body with food before you hit the gym; it's likely to suppress your appetite afterwards, so you'll eat less and save calories that way. As one study published in the journal Appetite revealed, the participants who had eaten pre-work out reported less of an urge to eat large portions of food later on in the day.

And if the motivation of your gym-going is all about building lean muscle, then working out on an empty stomach could be holding you back there, too. Fasted exercise can apparently lead to the shedding of muscle as well as the burning of fat. This could happen if your body has burned through its store of glycogen fuel and it's desperately seeking out energy to burn elsewhere - it'll look to the muscles. It's worth noting that this usually only occurs if a person seriously intensifies the amount of exercise they're doing, though.